JVM, JRE & JDK

Java Virtual Machine (JVM) :-

• It is the virtual machine that runs the java bytecodes.
• The JVM is called virtual because it provides a machine interface that does not depend on the underlying operating system and machine hardware architecture.This independence from hardware and the operating system is a corner-stone of the write-once-run-anywhere value of Java programs.
• JVM is also platform dependent and provides core java functions like memory management, garbage collection, security, etc.
• JVM is customizable and we can use java options to customize it, for example allocating minimum and maximum memory to JVM.
• The JVM performs the following main tasks:

1. Loads code
2. Verifies code
3. Execute code
4. Provides runtime environment

Java Runtime Environment (JRE) :-

• It is a software package that provides java class libraries, along with Java Virtual Machine (JVM), and other components to run applications written in Java programming.
• To execute any Java application, you need JRE installed in the machine. It's minimum requirement to execute java applications on any machine.
• JREs can be downloaded as a part of JDKs or you can download them separately.
• JREs are platform dependent. It means that based on the type of machine (OS and architecture), you will have to select the JRE bundle to import and install.

Java Development Kit (JDK) :-

• JDK contains everything that JRE has along with development tools for developing, debugging and monitoring Java applications.
• When you download JDK, JRE is also downloaded, and don't need to download it separately.
• Same as JREs, JDKs are also platform dependent.